The present invention relates to a rack and pinion type swing actuator with a backlash absorbing mechanism, and more particularly to a single rack type swing actuator which absorbs a backlash in an engaging portion between a rack and a pinion so as to remove a play in a rotational direction of the pinion.
Conventionally, there has been generally known a structure shown in FIGS. 4 and 5 as a backlash absorbing mechanism of this kind of rack and pinion type swing actuator.
FIG. 4 shows an embodiment of a backlash absorbing mechanism in a single rack type swing actuator having one rack. In this embodiment, a tooth portion 1a of a rack 1 and a tooth portion 2a of a pinion 2 are engaged with each other, and one end portion of an arm 5 synchronously rotating with the pinion 2 is fixed to the pinion 2. Accordingly, the structure is made such that a backlash in the engaging portion between the rack 1 and the pinion 2 is absorbed by bringing another end of the arm 5 mentioned above into contact with a stopper 4 so as to stop a rotation of the pinion 2 in a state of applying a propelling force in one direction to the rack 1 at an oscillating stroke end of the rack 1, whereby a play in a rotational direction of the pinion 2 is removed.
Further, FIG. 5 shows an embodiment of a backlash absorbing mechanism in a double rack type swing actuator having two racks. In this embodiment, a pair of racks 1 and 3 are arranged so as to hold the pinion 2 therebetween, tooth portions 1a and 3a of both of the racks 1 and 3 and a tooth portion 2a of the pinion 2 are engaged with each other, and the structure is made such that a backlash in the engaging portion between the rack 1 and the pinion 2 is absorbed by bringing one end of the rack 3 into contact with the stopper 4 so as to stop a rotation of the pinion 2 in a state of applying a propelling force in one direction to the rack 1 at a stroke end of the racks 1 and 3, whereby a play in a rotational direction of the pinion 2 is removed.
In this case, as mentioned above, in the case of the double rack type swing actuator, the backlash can be absorbed by the comparatively simple structure, however, in the case of the single rack type, since the arm 5 is fixed to the pinion 12 and the stopper 4 is used for stopping the rotation of the pinion 2, an outer size of the backlash absorbing mechanism is increased, the swing actuator is not well received, and the arm 5 is operated in a state of being protruded to an outer portion from the actuator, so that there are problems that a danger is generated and a safety can not be secured.
The present invention is made by taking the problems mentioned above into consideration, an object of the present invention is to provide a single rack type rack and pinion type swing actuator which can absorb a backlash in an engaging portion between a rack and a pinion by a simple structure and can remove a play in a rotational direction of the pinion.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a rack and pinion type rotary actuator comprising: a cylinder hole provided in a casing; end blocks closing both ends of the cylinder hole; one rack having pistons at both ends and sliding within the cylinder hole in accordance with an operation of a fluid pressure; a pinion rotating in a state of being engaged with the rack; pressure chambers respectively formed between the pistons at both ends of the rack and the end blocks; and ports for supplying a pressure fluid to the respective pressure chambers, wherein at least one of the rack and the pinion has stoppers in both sides of a tooth portion, the rack and the pinion has a relation that the rack and the pinion are engaged with each other by the stopper at both oscillating stroke ends of the rack, and the rack and each of the end blocks have a relation that the rack and each of the end blocks are not brought into contact with each other at the stroke end of the rack.
In the swing actuator in accordance with the present invention having the structure mentioned above, the rack and the pinion stop in a state of being engaged with each other by the stopper at the stroke end of the rack, whereby the pinion is prevented from being rotated. That is, a backlash in the engaging portion between the pinion and the rack is absorbed.
In accordance with a particular embodiment of the present invention, at least pinion of the rack and the pinion has the stopper, the pinion has the tooth portion having a plurality of teeth formed therein and a round portion having no teeth, and the stoppers are formed at positions adjacent to the tooth portions at both ends of the round portion.
In this case, preferably, an addendum circle in the tooth portion of the pinion and the round portion have the same radius, and the stopper is a flat surface inclined with respect to a radius of the round portion. Further, it is desirable to structure such that the rack has stoppers formed by a flat surface in both sides of the tooth portion, the rack and the pinion have the same number of teeth, and the stoppers of the rack and the stoppers of the pinion are in surface contact with each other at both stroke ends of the rack, respectively.
In accordance with another embodiment of the present invention, the rack has the stoppers in both sides of the tooth portion, and the pinion has the tooth portion in a whole periphery, whereby the rack and the pinion have a relation that the teeth of the pinion are engaged with the stopper at the stroke end of the rack.